The technology for manufacturing high strength and high hardness parts by heating powder compacts from metal powders without reaching the melting temperature is known under the name of Powder Metallurgy.
Bearing caps manufactured by Powder Metallurgy are known. This manufacturing technique allows a cost reduction and at the same times a better control of dimensions than in the case of similar parts manufactured by casting. These caps have the disadvantage that, after being assembled on the engine block, they have to be machined. This involves several problems because of different material characteristics that exist between these caps and the material of which the engine block is formed.
Generally bearing caps have a semi-cylindrical notch on one of their faces and they are provided with through orifices allowing fastening them by means of bolts to the engine block, which is also provided with semi-cylindrical notches complementary to the cap notches. The caps assembled on the engine block determine a series of hollow cylindrical portions where the bearings that support the crankshaft are located.
Dimensions and position of said hollow cylindrical portions must be of very high precision since a good engine function and especially the running noise, depend in a large extend upon the size, precision and alignment of these cylindrical portions. Therefore it is frequent to machine the different cylindrical portions formed by the caps and the engine block when they are assembled.
Due to the need to stop the manufacturing process for changing the tooling used for boring or machining of the caps and engine block system, most recent investigations aim at improving the machinability of the bearing cap manufactured by Powder Metallurgy without affecting its strength.
The document WO 0046520 describes a bearing cap composed by two powder conglomerates from different metal powder blends located within the part according to their different mechanical characteristics and the functionality of each portion of the part or cap. Thus the powder blend in the area adjacent to the semi-cylindrical notch differs from the powder blend of the rest of the part. This one is a powder blend, which provides said area with better machining characteristics, more similar to those of the engine block.
Manufacturing of these caps requires a complicated powder filling systems on the tool for compaction of the part before being heated or sintered, making possible to fill the tool with different blends and locating them within the corresponding areas during the compacting operation. This double filling process, also called “dual filling” becomes very complex and makes the manufacturing process of the caps significantly more expensive.
On the other hand, as stated in the same document, infiltration processes providing better characteristics for machining show advantages for a different kinds of parts or products, but they are not considered for the purpose of bearing caps.
Thus it is noticed the lack of a bearing cap, which even improving the strength of the known bearings caps, allows the extension of the useful life of the cutting tools used for machining the system composed by the bearing caps and the engine block.
The invention refers to a crackshaft bearing cap and its method for manufacturing, that provides a innovative and effective solution to the problems described above, allowing the extension of the useful life of the cutting tools of its mechanization